1. Field of the Invention
The invention is related to monitoring data transmissions, and more particularly, the invention is related to monitoring a facsimile transmission through a digital facsimile network.
2. Description of the Related Art
Conventionally, facsimile data transmissions are conducted entirely through voice grade, analog telephone lines. A typical facsimile transmission route is shown in FIG. 1. A source facsimile device 10 dials a phone number of a destination facsimile device 12. The call is routed through a telephone jack 20 to a local exchange carrier at a central office (LEC CO) 30. Subsequently, a connection is made from the LEC CO 30 to a local inter-exchange carrier's point of presence (IXC POP) 40. The local IXC POP 40 makes a connection through a long distance carrier facility 50 to a destination IXC POP 42 which in turn makes a connection to a destination LEC CO 32. The destination LEC CO 32 then calls the phone number of the destination facsimile device 12. Once the destination facsimile device 12 answers, an end-to-end connection is established between the two facsimile devices 10, 12. The appropriate facsimile session setup is then performed by the two facsimile devices 10, 12, and this is followed by the facsimile data transmissions. Upon completion of the facsimile data transmissions, the facsimile devices hang up and the connection is terminated.
In the conventional system illustrated in FIG. 1, when one facsimile device dials another, a circuit-like connection is created between the two devices. Data is transmitted between the devices in real-time. In other words, there is little delay from when the source facsimile device 10 sends data to when the destination facsimile device 12 receives the data.
Further in the conventional system, telecommunications services (phone lines, etc.) used for facsimile transmissions, and their associated cost structure, are formally defined by the carrier in a document called a tariff. Tariffs are filed for approval by state regulatory commissions and/or the Federal Communication Commission (FCC).
There are also store and forward services available for transmitted facsimiles. With store and forward, a facsimile is generally transmitted to a local vendor with information about the final destination. The local vendor then takes responsibility for delivering the facsimile. Such services are not real-time in that there is no circuit-like connection between the source and destination facsimile devices. In such systems, the facsimile transmission is usually sent at a later time when the rates are less. A disadvantage of such systems is that in the event a facsimile cannot be delivered to the destination facsimile device, there may be no reliable way of notifying the user of the source facsimile device that the facsimile has not been delivered. Important facsimile transmissions requiring immediate delivery and confirmation of receipt generally cannot be sent through such systems.
Another conventional way of reducing costs of data transmission including, for example, facsimile data, voice data, and modem data, is to use alternate communication services, such as a dedicated telephone lines such as a Wide Area Telephone Service (WATS) line. Alternatively, telephone companies offer a variety of overlapping discount schedules which could be utilized to minimize costs for a particular transmission. A disadvantage of using such alternate communication services is that a user has to be aware of a multitude of telephone number, access codes, and rate schedules.
As described above, facsimile transmissions today are accomplished through the use of analog grade circuits. The bandwidth of analog voice grade circuits is however very small and so telephone companies have migrated their equipment to provide their transmission services using a digital network. Nevertheless, access to the digital network is still made through voice grade lines and thus facsimile transmissions still need to be converted from analog to digital. The conversion from analog to digital involves a fairly high data rate, 64 Kilo-bits per second (Kbps), but the overall transmission speed is limited by the rate of transmission over the voice grade line, 9.6 Kbps or 14.4 Kbps. As a consequence, when a facsimile is sent over a voice grade circuit through the network's digital transmission facilities, most of the bandwidth is not utilized even though it is being paid for.
An example of the above-described digital network is shown in FIG. 2, and corresponds to a system recommended in a document published by The International Telegraph and Telephone Consultative Committee (CCITT). In the CCITT system, data is transmitted digitally between a source facsimile packet assembly/disassembly facility (FPAD) 44 and a destination FPAD 46 through a Packet Switched Public Data Network (PSPDN) 51. The access to either FPAD 44 or 46 is still made through its respective General Switched Telephone Network (GSTN) 31 or 33. The CCITT system has some technical characteristics, however, which make it unattractive, particularly for facsimile transmissions. They are:
1. It runs on X.25 protocol which significantly increases the length of call. PA1 2. It does not guarantee delivery of data. PA1 3. It has a variable delay in delivery of communicated packets. PA1 4. It does not accommodate switched analog access lines.